Following the footsteps of chance discoveries, which have dotted human history through the ages, a Neuroscience graduate student at the University of Rochester, who was reviewing data for one project accidentally found that in patients of Alzheimer’s disease, the location where plaques get deposited could contribute to hearing loss.
The Neuroscience graduate, Daxiang Na, working in the White Lab at the Del Monte Institute for Neuroscience at the University, was testing mice with amyloid beta, the major component of protein plaques and tangles implicated in Alzheimer's disease.
Working with two mouse models, Na found that in one of the models, called 5xFAD group, the elderly mice showed hearing changes similar to what is found among patients of Alzheimer's disease.
Na further found that this change was not there either in the younger 5xFAD group or the other group.
Commenting about the development Na who is the first author of a paper with these findings published in the journal Frontiers in Neuroscience, said, “It was a chance observation,”
“Both mouse models had amyloid beta protein, but where we found the plaque varied and that may be why hearing loss varied across the groups,” he postulated.
The research team found that the brains of older mice from both models had plaques in the hippocampus, a seahorse-shaped area at the centre of the brain well-known for its role in learning and memory by processing external stimuli, including sound and auditory cortex.
However, upon additional research, they discovered that the brains of mice with hearing problems had a small amount of plaque on the auditory brainstem, implying that this area may be sensitive to disturbance from plaque present in Alzheimer's patients.
According to the researchers, the plaque decreased the brainstem's ability to coordinate reactions to sound.
“This may explain why Alzheimer’s patients have auditory symptoms,” said Patricia White, PhD, professor of Neuroscience and senior author of the study.
Pointing out that the research team’s data suggest that regular auditory Brainstem Response assessments could help with diagnosis, she added, “We think the location of plaques may be more important to hearing decline. It could be a potential biomarker to track disease progression because it could be assessed with amyloid PET imaging.”
According to the 2022 Alzheimer's Association Report, while mortality from stroke, heart disease, and HIV declined between 2000 and 2019, reported deaths from Alzheimer's disease climbed by more than 145% during the same period.
Furthermore, in 2021 alone, over 11 million family members and other unpaid carers supplied an estimated 16 billion hours of care to persons with Alzheimer's or other dementias, emphasising the severity of the disorder.
The findings have a substantial bearing among Indians as according to a 2023 collaborative study published in the Alzheimer's & Dementia the researchers estimated that about 8.8 million Indians older than 60 years living with dementia, primarily caused by AD.
Furthermore, in a meta-analysis published in the National Medical Journal of India, the researchers found that about half of those over 60 years of age in the country suffer from disabling hearing loss.
Experts estimate that in India approximately four million AD patients might be suffering from hearing loss.
However, ignorance about the problems, a lack of access to facilities, and financial constraints resulting in delayed or no treatment is putting a further burden on the caregivers, primarily untrained and unpaid.
Researchers fear that in the coming decades, the Indian population as Indian population starts ageing further and matching that of the developed countries both these conditions are going to create will mature and a population pyramid similar to that of more industrialised countries. An ageing population will throw a considerably bigger load on India's healthcare infrastructure.